[wxPython-users] Re: Trouble with drawing, I need some ideas :)

[Robin Dunn]

Peter Damoc wrote:
> Problem solved via:
> 
> def SetAlpha(bmp):
>     w, h = bmp.GetSize()
>     img = bmp.ConvertToImage()
>     img.InitAlpha()
>     for i in range(w):
>         for j in range(h):
>             img.SetAlpha(i,j, 0)
>     return img.ConvertToBitmap()
> 
> Ugly hack but... until I find something better.... :) will have to do...

I was just chatting with a coworker at OSAF about a similar problem, and 
I realized that this is probably equivalent to how you are using the 
above.  It creates a new bitmap with all pixels set to black and with a 
fully transparent alpha:

	bytes = array.array('B', [0] * width*height*4)
	bmp = wx.BitmapFromBufferRGBA(width, height, bytes)

Then any drawing you do on it with a wx.GCDC or a wx.GraphicsContext 
will be working on a fully transparent background, and will reset the 
alpha as as specified in the pen or brush objects when drawing other 
things on top of it.

-- 
Robin Dunn
Software Craftsman
http://wxPython.org  Java give you jitters?  Relax with wxPython!